[BRUSHFIRE](https://attack.mitre.org/software/S9011) is a passive backdoor written in C that executes in-memory within an existing process. First reported in March 2025, [BRUSHFIRE](https://attack.mitre.org/software/S9011) has been observed in activity attributed to People's Republic of China (PRC) state-affiliated threat actors, including UNC5221 and SYLVANITE.(Citation: Dragos SYLVANITE MuddyWater Electrum March 2026)(Citation: Google UNC5221 Ivanti April 2025)(Citation: Picus Security UNC5221 Ivanti May 2025)